Marine Sediment Mixed With Activated Carbon Allows Electricity Production and Storage From Internal and External Energy Sources: A New Rechargeable Bio-Battery With Bi-Directional Electron Transfer Properties

SMFC as a tool for the removal of hydrocarbons and metals in the marine environment: a concise research update

Marine pollution is becoming more and more serious, especially in coastal areas. Because of the sequestration and consequent accumulation of pollutants in sediments (mainly organic compounds and heavy metals), marine environment restoration cannot exempt from effective remediation of sediments themselves. It has been well proven that, after entering into the seawater, these pollutants are biotransformed into their metabolites, which may be more toxic than their parent molecules. Based on their bioavailability and toxic nature, these compounds may accumulate into the living cells of marine organisms. Pollutants bioaccumulation and biomagnification along the marine food chain lead to seafood contamination and human health hazards. Nowadays, different technologies are available for sediment remediation, such as physicochemical, biological, and bioelectrochemical processes. This paper gives an overview of the most recent techniques for marine sediment remediation while presenting sediment-based microbial fuel cells (SMFCs). We discuss the issues, the progress, and future perspectives of SMFC application to the removal of hydrocarbons and metals in the marine environment with concurrent energy production. We give an insight into the possible mechanisms leading to sediment remediation, SMFC energy balance, and future exploitation.

Scale-up and control the voltage of sediment microbial fuel cell for charging a cell phone

In this research, a power management system (PMS) has been developed to charge a cell phone battery based on sediment microbial fuel cells (SMFCs). The single SMFC produces a voltage of 1.16 V, which is too low for practical application. The voltage is increased by connecting several SMFCs in series or parallel, but the voltage reversal occurs when it is directly connected to the load. To prevent the voltage reversal, the super capacitor is first charged by the five different stack SMFCs and the charged super capacitor is used to provide the input power to a PMS. This PMS increases and regulates the input voltage of stack SMFCs up to 5.02 V for charging a cell phone battery. The charging and discharging times of the super capacitors have been investigated with five different stack SMFCs. In all five stack SMFCs, only module-5 provides power to PMS for long periods (13 min). Further, the cell phone battery is continuously charged using the two parallel-connected stack SMFCs similar to the module-5. The battery has been fully charged in 26 h using 72 SMFCs. The charged battery is used to perform for three purposes; voice calling, music playing and LED strip lighting. This study is informative for the application of SMFC in an off-grid location.

Aggregation-dependent electron transfer via redox-active biochar particles stimulate microbial ferrihydrite reduction

Microbial Fe(III) reduction plays an important role for biogeochemical carbon and iron cycling in sediments and soils. Biochar is used as a soil amendment to increase fertility and lower N₂O/CO₂ emissions. It is redox-active and can stimulate microbial Fe(III) mineral reduction. It is currently unknown, however, how the aggregation of cells and Fe(III) minerals with biochar particles influence microbial Fe(III) reduction. Therefore, we determined rates and extent of ferrihydrite (Fh) reduction in S. oneidensis MR-1 cell suspensions with different particles sizes of wood-derived Swiss biochar and KonTiki biochar at different biochar/Fh ratios. We found that at small biochar particle size and high biochar/Fh ratios, the biochar, MR-1 cells and Fh closely aggregated, therefore addition of biochar stimulated electron transfer and microbial Fh reduction. In contrast, large biochar particles and low biochar/Fh ratios inhibited the electron transfer and Fe(III) reduction due to the lack of effective aggregation. These results suggest that for stimulating Fh reduction, a certain biochar particle size and biochar/Fh ratio is necessary leading to a close aggregation of all phases. This aggregation favors electron transfer from cells to Fh via redox cycling of the electron donating and accepting functional groups of biochar and via direct electron transfer through conductive biochar carbon matrices. These findings improve our understanding of electron transfer between microorganisms and Fe(III) minerals via redox-active biochar and help to evaluate the impact of biochar on electron transfer processes in the environment.

A Thin Layer of Activated Carbon Deposited on Polyurethane Cube Leads to New Conductive Bioanode for (Plant) Microbial Fuel Cell

Large-scale implementation of (plant) microbial fuel cells is greatly limited by high electrode costs. In this work, the potential of exploiting electrochemically active self-assembled biofilms in fabricating three-dimensional bioelectrodes for (plant) microbial fuel cells with minimum use of electrode materials was studied. Three-dimensional robust bioanodes were successfully developed with inexpensive polyurethane foams (PU) and activated carbon (AC). The PU/AC electrode bases were fabricated via a water-based sorption of AC particles on the surface of the PU cubes. The electrical current was enhanced by growth of bacteria on the PU/AC bioanode while sole current collectors produced minor current. Growth and electrochemical activity of the biofilm were shown with SEM imaging and DNA sequencing of the microbial community. The electric conductivity of the PU/AC electrode enhanced over time during bioanode development. The maximum current and power density of an acetate fed MFC reached 3 mA·m−2 projected surface area of anode compartment and 22 mW·m−3 anode compartment. The field test of the Plant-MFC reached a maximum performance of 0.9 mW·m−2 plant growth area (PGA) at a current density of 5.6 mA·m−2 PGA. A paddy field test showed that the PU/AC electrode was suitable as an anode material in combination with a graphite felt cathode. Finally, this study offers insights on the role of electrochemically active biofilms as natural enhancers of the conductivity of electrodes and as transformers of inert low-cost electrode materials into living electron acceptors.

Activated Carbon Mixed with Marine Sediment is Suitable as Bioanode Material for Spartina anglica Sediment/Plant Microbial Fuel Cell: Plant Growth, Electricity Generation, and Spatial Microbial Community Diversity

Wetlands cover a significant part of the world’s land surface area. Wetlands are permanently or temporarily inundated with water and rich in nutrients. Therefore, wetlands equipped with Plant-Microbial Fuel Cells (Plant-MFC) can provide a new source of electricity by converting organic matter with the help of electrochemically active bacteria. In addition, sediments provide a source of electron donors to generate electricity from available (organic) matters. Eight lab-wetlands systems in the shape of flat-plate Plant-MFC were constructed. Here, four wetland compositions with activated carbon and/or marine sediment functioning as anodes were investigated for their suitability as a bioanode in a Plant-MFC system. Results show that Spartina anglica grew in all of the plant-MFCs, although the growth was less fertile in the 100% activated carbon (AC100) Plant-MFC. Based on long-term performance (2 weeks) under 1000 ohm external load, the 33% activated carbon (AC33) Plant-MFC outperformed the other plant-MFCs in terms of current density (16.1 mA/m2 plant growth area) and power density (1.04 mW/m2 plant growth area). Results also show a high diversity of microbial communities dominated by Proteobacteria with 42.5%–69.7% relative abundance. Principal Coordinates Analysis shows clear different bacterial communities between 100% marine sediment (MS100) Plant-MFC and AC33 Plant-MFC. This result indicates that the bacterial communities were affected by the anode composition. In addition, small worms (Annelida phylum) were found to live around the plant roots within the anode of the wetland with MS100. These findings show that the mixture of activated carbon and marine sediment are suitable material for bioanodes and could be useful for the application of Plant-MFC in a real wetland. Moreover, the usage of activated carbon could provide an additional function like wetland remediation or restoration, and even coastal protection.